A phase locked loop (PLL) is electronic circuitry commonly used in applications involving communications, computers and other electronic systems. For example, it is known that PLLs are typically used in the read and write channels of a hard disk drive. A hard disk drive is a non-volatile storage device which stores digitally encoded data on one or more rapidly rotating platters with magnetic surfaces, collectively referred to as the “disk.” The read channel comprises circuitry for reading data from the disk in response to one or more read commands, while the write channel comprises circuitry for writing data to the disk in response to one or more write commands.
The PLL generally includes a variable frequency oscillator. The variable frequency oscillator is typically designed as an inductor-capacitor (LC) tank based voltage controlled oscillator (VCO), in which the frequency is varied by controlling the value of the tuning capacitor using a voltage dependent capacitance or varactor.